1. Field of the Invention
The present invention relates to a multi-stage complementary metal oxide semiconductor (CMOS) power amplifier applicable to a mobile communications system such as a mobile phone, and more particularly, to a multi-stage CMOS power amplifier having enhanced power efficiency by improving power matching among plural amplifiers included in the multi-stage CMOS power amplifier.
2. Description of the Related Art
Generally, in order to extend continuous call time in a mobile phone, the efficiency of a power amplifier that amplifies microwaves sent to a base station is very important. In this regard, a multi-stage power amplifier in which plural power amplifiers are connected in a cascade may be used.
Also, when a power amplifier for a mobile phone is designed by using a complementary metal oxide semiconductor (CMOS) process widely used in a specific GaAs semiconductor production process, it can be mass produced. Accordingly, there are the advantages of reduced production costs and multi functionality.
A conventional multi-stage CMOS power amplifier, as mentioned above, may be configured in such a manner that plural power amplifiers are connected in a cascade.
More specifically, the conventional multi-stage CMOS power amplifier may include a driver amplifier and a power amplifier, for example, each of which has a differential configuration such that each amplifies signals having different phases.
Each of the amplifiers included in the power amplifier having a differential configuration may include at least one metal oxide semiconductor (MOS) transistor in order to amplify an input alternating voltage.
In such a conventional multi-stage CMOS power amplifier, however, since the MOS transistor included in the power amplifier performs turn-on and turn-off operations on the basis of an alternating voltage of 0.4V, when the input alternating voltage is above 0.8V, voltage waveform is distorted. Accordingly, the amplifying rate is reduced, and thus power efficiency is degraded.